In continuing our studies of the nature and origins of antibiotic resistance in clinical isolates of bacteria, we have made the following progress: 1) Bacteriophage lambda lines carrying kanamycin and other resistance determinants have been obtained by transposing resistance determinants by selection, subsequent to infecting an R positive strain lacking a normal lambda attachment site. The transposons characterized by electron microscopy and restriction endonuclease analysis have been shown to consist of an inverted repeat (is) sequence and terminal loop. These phages will be used in hybridization studies. 2) Preparatory to attempts to demonstrate similarities between resistance determinants on R factors and Staph plasmids, we have characterized the neomycin phosphotransferases of several clinical isolates of Staphylococcus. 3) Kanamycin acetyltransferase has been partially purified and is being used to prepare rabbit antisera. This enzyme, and its expression in a number of different bacterial strains, has been studied extensively. BIBLIOGRAPHIC REFERENCES: Thammana, P., and Davies, J., Sensitivity and resistance to the antibiotic Kausugamycin in E. coli, In Drug Resistance and Drug Action in Bacteria (S. Mitsuhashi, ed.), University of Tokyo Press, 1975, p. 249-268. Haas, M., Biddlecome, S., Davies, J., Luce, C. E. and Daniels, P. J. L. Enzyme modification of aminoglycoside antibiotics; a new 6'-N-acetylating enzyme from a P. aeruginosa isolate, 1976, in press in Antimicrobial Agents and Chemotherapy.